Hybrid electric vehicles utilizing both an electric motor/generator and an internal combustion engine as power sources often have an onboard electronic controller programmed to vary the use of the engine and motor/generator during different driving conditions to achieve peak efficiency. One type of hybrid electric vehicle is referred to as a belt-alternator-starter (BAS) hybrid vehicle. This type of vehicle may have a motor/generator operatively connected to an engine crankshaft by a belt and pulley system. The motor/generator in a BAS hybrid vehicle may be used to start the engine from a key start and may be recharged by the engine during regenerative braking BAS hybrids are sometimes controlled to provide an engine auto-stop when vehicle speed is zero but the key is in the run position, such as when the vehicle is stopped at a stop light. An engine “auto-stop” is a controlled stop of the engine that brings the rotational speed of the crankshaft to zero when the key is still in the run position. The engine is then started by the motor/generator when propulsion is desired, as may be indicated by a lifting of a brake pedal. This type of start is referred to as an “auto-start”.
Engine creep torque is the relatively low drive torque transmitted to the drive axle due to rotational speed of the engine when the accelerator pedal is not depressed and the engine rotation is mechanically coupled to the drive wheels via some torque transmission device such as a hydraulic torque converter commonly utilized in automatic transmission equipped vehicles. Engine creep torque will cause a vehicle to creep forward at a very low speed if neither the accelerator pedal nor the brake pedal is depressed. When vehicle speeds are relatively low and neither the brake nor accelerator pedals are applied, engine creep torque is the predominant motive vehicle force and changes in engine creep torque are noticeable to a vehicle operator.